Should You Double Dip?

The dreaded communal salsa bowl.  At a large gathering or party, who knows how many people have double dipped or even triple dipped?! It is a well-known idea that double-dipping is nasty and should only occur when there is only one person eating from the dish.  I wanted to know more of the science behind double dipping and if it is worth it. Personally, I think it is very likely that double-dipping adds bacteria to the food, since a person makes contact with the bacteria in their mouth and proceeds to put it back in the food.  

 Researchers at Clemson University set out to determine if double dipping adds germs and bacteria to food.  The study was composed of three separate experiments to determine this answer.  One of the experiments they performed had eight people submerse crackers into water, with some taking a bite prior to dipping, in order to see if double dipping alters bacteria levels.   After this experiment was performed, the concluding data shows significantly higher levels of bacteria when the cracker was bitten before dipped as opposed to the others who did not bite it prior to dipping it into the water.  A “P” value is provided in the abstract of this experiment and is less than 5%.  This means that given the values of the data, it is very unlikely that these results are a fluke, although they could still be due to chance.  Initially it stands out to me that this particular experiment only had eight people in total, which reduces the reliability of the experiment.

The second experiment performed on this subject was similar, but tested the pH of common dips that are victims of double dipping- including salsa, chocolate sauce, and cheese sauce.  The results remain consistent with the first experiment: there were higher levels of bacteria in the double dipped solutions than the untouched solutions.  Although, the salsa had more bacteria than the chocolate sauce and cheese sauce solutions.  This could either be a fluke or an experimental error, but there is no mechanism provided for why the salsa has higher bacteria.  

These experiments were two of three performed in this study in order to find out whether double dipping makes a difference in bacteria in food or if it’s not a big deal.  The third experiment was very similar to the second experiment, with consistent results as the preceding two. This is the only study I could find that had a reliable design.  Although, the study could have been larger, the results remain consistent with my hypothesis that double dipping adds bacteria to a food dish.

Although the study concludes with elevated bacteria levels in double-dipped dishes, these are soft endpoints because it would only increase the level of bacteria in the food, which people believe could make them sick.  Bacteria is everywhere, so there is no way to avoid consuming bacteria even if you do not double dip because there are many other ways these bacteria can be spread (e.g. coughing).  With this study, the null hypothesis, that double dipping does not increase bacteria levels in food, is rejected due to the increase in levels of bacteria.

To summarize, double dipping does add more bacteria to food than is already there.  In the end, it is not worth it to double dip because although you may not be affected, those who come after you will be affected also.  Not to mention someone could have double dipped before you got there!

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5 thoughts on “Should You Double Dip?

  1. Griffin Lambert Brooks

    Personally, its bad to say but I have always been a double dipper. I know it’s slightly disgusting for other people who are sharing the same dip, but how when you’re eating Tostitos and salsa are you supposed to eat the Tostito in one bite and get a good proportion of salsa with it! I know I can’t eat a whole Tostito in one bite because they’re too big and not manageable to put in your mouth in one bite, so thats why I double dip, so the second bite also has salsa on it and tastes just as good as the first bite. After reading your blog I found it interesting but not surprising that double dipping causes bacteria to increase and more germs to be spread. Looking back on it double dipping is gross and people like myself shouldn’t do it because it gives others a higher risk to catch germs and illness. Don’t double dip!

  2. Monica Lynn Powell

    I really enjoyed this blog, being a germaphobe myself! I liked how you consulted several different studies in order to gain the most information that you could. I was curious as to what the pH levels meant in accordance with the bacteria. Why was that being tested and what did that show? I think you did a great job with pulling in concepts from class and also evaluating the strength of the studies in which you talked about. The one study had a small sample size and I was glad that you made note of that. Do you think the study would have gotten stronger results if they had done more trials? When it comes to germs, for me at least, there doesn’t need to be a mechanism to explain it all. I don’t like being sick, therefore I don’t like germs and despite there not being a mechanism I won’t be double dipping. Though the evidence wasn’t super strong, double dipping is such an easy thing to stop….just to be safe! Here’s an article that gives ideas as to how to politely ask people not double dip and spread germs!

    1. Lydia A Chelli Post author

      Thanks for commenting! You mentioned you did not see how pH played out relating to the bacteria in the second experiment. Since the scientists wanted to compare the bacteria levels of the three dips (salsa, chocolate sauce, and cheese) after double dipping, they tested the pH of each of these dips. After learning the pH levels of each dip, they altered the pH of water to the pH of the dips in order to simplify the process of the experiment. In my opinion, a benefit to using water as the material to test the dependent variable is that the scientists can measure the water easier than testing chunky salsa.
      If the study had more trials, then it would make the evidence and data more reliable if there was an abundance of consistent data. I do agree that the evidence was not very strong, and did a great deal of research in order to find more experiments to either support or go against my hypothesis and the results I found. Even if the data regarding the topic of double dipping is not very strong, we have discussed in class that a logical person mind as well not double dip since it may benefit and does not risk him/her.

  3. Abigail Roe

    Lydia, this is an intriguing blog post, but surprisingly I am not offset by your findings. It is evident that everyone has different germs and bacteria, so if one person double dips in a communal bowl of dip it is bound to be slightly contaminated. Your post was sufficient with studies and evidence. Your first study had a narrow experimental group, but you clarified that in your post. Were there any other studies done that had a larger group to experiment on? I like how you used some terminology from class, such as the “P value.” While reading about the second study you discussed, I accumulated some questions. You said they were testing the pH level of the different dips. What dips were more likely to manifest bacteria from double dipping? Ones with a higher level of pH or lower level of pH? I am sure that this is not a severe case of contamination. The manifested bacteria might have something to do with the number of people who double dip as well. However, I wonder if someone could get mono from double dipping? If someone who has mono double dipped, would other people who dipped as well be likely to get the disease? I looked into mono and the concept of how it is passed from person to person. Mono is spread by the sharing of saliva. Here is an article about mono and the ways it can be spread.

    1. Lydia A Chelli Post author

      I searched for more detailed and larger studies relating to this topic, but most of them were insufficient and/or unreliable. As I mentioned in my post, it was found that the pH of salsa had higher bacteria levels than the other two sauces. I excluded in my post that this was the lowest pH of the other sauces tested. Thanks for asking! Since you mentioned mono is spread by the sharing of saliva, I can only imagine that one could catch it through double dipping.

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